An HTS cable demonstration project has started in 2007. The cable has 66kV/200MVA capacity and 200-300m length. It will be installed and operated at Asahi sub-station in Yokohama in 2011. Bismuth-based HTS wires with twisted superconducting filaments are used for the cable to reduce the AC loss. In 2009, a 30m cable system has been constructed and tested to verify the assembling technologies of the cable, a joint and terminations and their performance. This paper describes the overview and current status of this project.
In correspondence with the development of the high information-oriented society, macroscale of the information voltage by the optical fiber is planned. In such situation, it is OPGW forming the basis of the current communication. I introduce process about this development.
The purpose of this study is to estimate eigen-values and eigen-vectors of a power system from on-line data to evaluate the power system stability. Power system responses due to the small power modulation of known pattern from SMES (Superconducting Magnetic Energy Storage) were analyzed, and the transfer functions between the power modulation and power oscillations of generators were obtained. Eigen-values and eigen-vectors were estimated from the transfer functions. Experiments were carried out by use of a model SMES and Advanced Power System Analyzer (APSA), which is an analogue type power system simulator of Kansai Electric Power Company Inc., Japan. Changes in system condition were observed by the estimated eigen-values and eigen-vectors. Result agreed well with the resent report and digital simulation. This method gives a new application for SMES, which will be installed for improving electric power quality.
An imbalanced current distribution is often observed in cable-in-conduit (CIC) superconductors which are composed of multi-staged, triplet type sub-cables, and hence deteriorates the performance of the coils. Therefore, since it is very important to obtain a homogeneous current distribution in the superconducting strands, we propose a coaxial multi-layer type CIC conductor. We use a circuit model for all layers in the coaxial multi-layer CIC conductor, and derive a generalized formula governing the current distribution as explicit functions of the superconductor construction parameters, such as twist pitch, twist direction, radius of each layer, and number of superconducting (SC) strands and copper (Cu) strands. We apply the formula to design the coaxial multi-layer CIC which has the same number of SC strands and Cu strands of the CIC for Central Solenoid of ITER. We can design three kinds of the coaxial multi-layer CIC depending on distribution of SC and Cu strands on all layers. It is shown that the SC strand volume should be optimized as a function of SC and Cu strand distribution on the layers.
Controlling the current distribution in each layer of a co-axial multi-layered high-Tc superconducting (HTS) cable uniformly is important in order to realize a compact and large capacity HTS power cable. The phenomenon of current imbalance should be exactly investigated by the analysis, because the current imbalance causes an increase of AC loss. In this paper, 3-D finite element analysis taking account of the nonlinear E-J characteristic is carried out in order to study the AC loss of a co-axial multi-layered HTS power cable with shield layers. The analysis region is considerably reduced by modeling spirally wound superconducting tapes as conductors having an anisotropic conductivity and using the periodic boundary condition. By using this model, AC transport characteristics of the co-axial three-layers cable (composed of two conductor layers and one shield layer) are studied, and the AC loss is investigated. The structure with low AC loss is also discussed.
In large-scale SMES, the superconducting coils require special considerations for induced electromagnetic forces to limit allowable tensile stress. Force-balanced coil (FBC) is a helically wound hybrid coil of toroidal field coils and a solenoid. The FBC can significantly reduce the required mass of the structure for induced electromagnetic forces. In order to demonstrate the feasibility of the FBC concept for SMES, the authors have developed a superconducting model coil. The outer diameter of the model FBC is 0.53m. The hand-made winding, using NbTi/Cu composite strands with a diameter of 1.17mm, was finished with 10584 poloidal turns after four months. The helical windings of the model FBC were neither impregnated with epoxy resin nor reinforced with stainless steel wires. Three test runs were conducted with liquid helium cooling at intervals of several months. The number of quench tests was 81 in total. The first quench current was 293A, which was 53% of the critical coil current. The training phenomena could be observed even after the coil was warmed up to room temperature. After successive quenches the quench current was improved to 476A, corresponding to 86% of the critical coil current, and it was successfully excited up to 6.1T.
Voltage dips of power grids due to thunderbolts, snow damage, and so on, cause serious damage to production lines of precision instruments, for example, semiconductors. In recent years, in order to solve this problem, uninterruptible power supply systems (UPS) are used. UPS, however, has small capacity, so a great number of UPS are needed in large factories. Therefore, we have manufactured the superconducting magnetic energy storage (SMES) system for voltage dip compensation able to protect loads with large capacity collectively. SMES has advantages such as space conservation, long lifetime and others. In field tests, cooperating with CHUBU Electric Power Co., Inc. we proved that SMES is valuable for compensating voltage dips. Since 2007, 10MVA SMES improved from field test machines has been running in a domestic liquid crystal display plant, and in 2008, it protected plant loads from a number of voltage dips. In this paper, we report the action principle and components of the improved SMES for voltage dip compensation, and examples of waveforms when 10MVA SMES compensated voltage dips.
Each superconducting coil manufacturing process using YBCO tape coated conductor was evaluated, and double pancake type copper stabilized coils were verified, in order to develop base technologies of a YBCO coil for power applications. Cost of YBCO tape including a stabilization process needs to be low in order for it to be a practical use wire for power application coils. Conduction cooling is also needed below the 50K temperature range, which is optimal for high magnetic field coils using YBCO tape. Therefore, we developed technology for each process for manufacturing of a conduction cooling type coil. Techniques for winding, stabilization, electrode formation, and impregnation were developed, considering YBCO tape configuration and a conduction cooling method. Several wire coils were then manufactured and verified using a conduction cooling system, and the high performances of thermal stability, low electrical joint resistance, etc. were achieved without degradation.
When many distributed generators (DGs) are connected to a distribution line, the upward power flow from DGs causes the difficulty in line voltage regulation. As the countermeasure, we propose several methods to control the line voltage by use of DGs' reactive power outputs. These methods using only DGs' reactive power are implemented in an autonomous decentralized way. DGs with the function to estimate the line impedance provide the power system with reactive power according to the estimated impedance value, and regulate the line voltage. We evaluate the effect of the proposed methods for voltage compensation by experimental studies using commercial grid-connected inverters for PV system.
In the power sector, total capacity of wind power generations has been increasing drastically. However, the wind power affects the power grid frequency and the tie-line flow adversely because of the instability of output. In particular, these problems become significant at nighttime when the capacity of Load Frequency Control (LFC) tends to be insufficient. On the other hand, in the transport sector, Plug-in Hybrid Electric Vehicle (PHEV) is being developed as environmentally friendly vehicles. The electric energy of PHEVs is charged mainly during nighttime. Therefore, we have proposed a charging power control of PHEVs to compensate the LFC capacity in the nighttime. In this study, we propose a control method based on frequency characteristic of PHEV KPHEV, which is defined as a ratio of the change in charging power to the change in frequency. Area Requirement (AR) calculated by the LFC system is a required increment in generation; hence, we can also keep the balance of supply-and-demand by decreasing as much demand as AR. LFC signal fshift calculated by the following equation fshift = -AR/KPHEV is transmitted to all PHEVs in the area; then, PHEVs control the charging power on the basis of input signal. We evaluated the proposed control method by using an interconnected 2-area model and obtained the following results. Charging power control based on the proposed method can effectively suppress the tie-line flow deviation and it could substitute for LFC capacity.
This paper describes a novel power system which consists of distributed energy resources (DER) with a static switch at the point of common coupling. Usage of the static switch with a parallel processing control is a new application of line interactive type uninterruptible power supply (UPS). In recent years, various ways of design, operation, and control methods have been studied in order to find more effective ways to utilize renewable energy and to reduce impact for environment. One of features of a proposed power system can interconnect to existing utility grid without interruption. Electrical power distribution to the loads by the power system can be continued between the states of interconnection and isolate operation seamlessly. The novel power system has other benefits such as more efficiency, demand site management, easy to control power system inside, improvement of reliability for power distribution, the minimum requirement of protection relays for grid interconnection. The proposed power system has been operated with the actual loads of 20kW in the campus of the Aichi Institute of Technology since 2007.
This paper presents a novel method to analyze the optimal generation mix based on portfolio theory with considering the basic condition for power supply, which means that electricity generation corresponds with load curve. The optimization of portfolio is integrated with the calculation of a capacity factor of each generation in order to satisfy the basic condition for power supply. Besides, each generation is considered to be an asset, and risks of the generation asset both in its operation period and construction period are considered. Environmental measures are evaluated through restriction of CO2 emissions, which are indicated by CO2 price. Numerical examples show the optimal generation mix according to risks such as the deviation of capacity factor of nuclear power or restriction of CO2 emissions, the possibility of introduction of clean coal technology (IGCC, CCS) or renewable energy, and so on. The results of this work will be possibly applied as setting the target of the generation mix for the future according to prospects of risks of each generation and restrictions of CO2 emissions.
Recently, control engineering changes from classical control theory to modern control theory, and analogue to digital. However, as a matter of fact, the sensitivity adjustment of the parameters using Bode diagram require many time and works. In this paper, the tool of Matlab/Simulink that adjusted the AVR control parameter of the PI control type brushless and Thyristor excitation method by using the technique for based on the parameter space planning method by QE was made. Moreover, the adjustment of the sensitivity parameter of the excitation control method intended for the dynamic stability level area in Single Machine Infinite Bus is examined with the tool.
This paper describes synchronized injection method of distributed inter-harmonic currents, and inspection of new islanding operation detection method for clustering installation as its application. If small distributed generators (DG) interconnected with low voltage system are installed under clustering, when a intersystem fault occur between high and low voltage grid, islanding phenomena will pose a problem. The following methods are conventionally considered as a measure. (1) Method by distribution system facilities (2) Application of conventional islanding detection method (indirect detection of earth fault) However, the subject of maintenance of a system occurs by (1). The subject to which detection time becomes long depending on system conditions can be considered by (2). Then, in order to solve these subjects, we developed this new method.
This paper proposes new concept concerning the residual life of a power equipment group. The expectancy life of equipment group (defined as ‘equipment-residual-life’ in this paper) is gradually approach to zero as time passing just as like ‘human-life’. If the worn-out equipment replaces by new one successively for substituting its role in the power system, the residual life of equipment group up to the replacement time (defined as ‘replacement-residual-life’ in this paper) converges to the half of equipment mean life. This paper analyses the stochastic property and the yearly change of the equipment-residual-life and the replacement-residual-life by assuming the normal probability density function as the equipment life distribution. The typical simulations are illustrated for verifying the stochastic approaches and for discussing the related maintenance management.
Electric power demand has an increasing tendency year by year. The fluctuation of the electric power causes further increase in the cost of the electric power facility and electricity charges. The development of the electric power-leveling systems (EPLS) using energy storage technology is desired to improve the electric power quality. The EPLS with a SMES is proposed as one of the countermeasures for the electric power quality improvement. However, the SMES is very expensive and it is difficult to decide the gains of the controller. It is essential in the practical use that the reduction of SMES capacity is realized. This paper proposes a new optimization method of the EPLS. The proposed algorithm is hybrid architecture with a combination of SimE (Simulated Evolution) and GA (Genetic Algorithms). The optimization of the EPLS can be achieved by the proposed hybrid algorithm compared to the SimE and the GA.
We have developed a new environment-conscious transformer impregnated with vegetable based insulating oil which called PFAE (Palm Fatty Acid Ester). PFAE has 0.6 times less viscosity and 1.3 times higher dielectric constant compared to mineral oil. This means that a PFAE immersed transformer has better cooling efficiency and better insulating performance in paper-and-oil composite insulation systems, resulting in size reduction in comparison to conventional mineral oil immersed transformers. In this paper, insulating performance of lead to plane electrode models, cooling performance of a PFAE immersed transformer, and the result of analytical study of dissolved gas for abnormal diagnosis are described.
This paper discusses voltage control techniques for a self-excited induction generator, enabling constant voltage generation to wind speed variation across a wide range. Generated voltage in self-excited induction generators is dependent on the speed of rotation, which has meant that they could only be operated within a relatively narrow wind speed range. A leading-phase current capacitor can be used together with the variable reactor proposed in this paper to control reactive power input to a generator. The new voltage control system expands the wind speed range within which power generation is possible to about three times its present range.
In this paper, a new technique is proposed for distance relays setting in presence of Interline Power Flow Controller (IPFC). IPFC presence in power network impacts on conventional protection systems, particularly distance relays. The main impact of IPFC on distance relays is to deviate impedance region seen by distance relays from relays tripping characteristic. The proposed technique employs active and reactive power injected by series converter to adjust distance relay first zone boundaries by mapping so that the new boundary has the most overlap with impedance region. Since the technique needs off-line calculations, it does not impose significant computational burden on the relay during the fault. The efficiency of the proposed technique is shown by simulation results of a four bus system containing a two-converter IPFC.
The Japanese Electrotechnical Committee (JEC) of surge arresters has made great efforts to establish several new standards of metal-oxide surge arresters (MOSA), because the dramatic and continuous advance in the MOSA technology over the last 30 years required the new and improved test methods in succession. In the study to establish these standards, how to evaluate the MOSA performance against the energy duties has been usually the main topic because the energy duties are significantly related to the size of zinc-oxide elements and the construction of MOSA. This paper describes the concept and features of arrester operating duty tests in the JEC standards comparing with that in the standard of the International Electrotechnical Commission (IEC) and also mentions the points at issues to be studied in the future which is common to both the JEC and IEC standards. The continuous study on the improvement of the standards is required in cooperation with the activities of IEC and the Internaltional Council on Large Electric Systems (CIGRE: Conseil International des Grands Reseaux Electriques) taking into account of the latest world trend and the state-of-the-art technologies.